[ AEEP2211 ] Lab 5

B

What is a separately-excited DC motor?

A. A motor where the armature is supplied separately

B. A motor where the field winding is supplied by a separate DC source

C. A motor that uses only permanent magnets

D. A motor supplied only by AC

A

What is the purpose of the field current?

A. To create the magnetic field

B. To control armature resistance

C. To produce the mechanical load

D. To measure motor speed

C

What does EA represent?

A. Armature current

B. Armature resistance

C. Armature voltage

D. Field voltage

A

What does IA represent?

A. Armature current

B. Field current

C. Motor speed

D. Armature voltage

B

What does RA represent?

A. Rotor speed

B. Armature resistance

C. Field resistance

D. Mechanical resistance

C

What is ECEMF?

A. The voltage drop across the resistor

B. The voltage applied to the motor

C. The induced voltage produced when the motor rotates

D. The field voltage

B

What happens to ECEMF when motor speed increases?

A. It decreases

B. It increases

C. It stays constant

D. It becomes zero

A

What is the relationship between motor speed and ECEMF?

A. n = K1ECEMF

B. n = K2IA

C. n = RAIA

D. n = ECEMF/K2

B

What is the relationship between motor torque and armature current?

A. T = K1ECEMF

B. T = K2IA

C. T = RAIA

D. T = EAIA

B

What happens to motor torque when armature current increases?

A. It decreases

B. It increases

C. It stays constant

D. It becomes zero

B

What is the voltage drop across the armature resistance?

A. ERA = RA/IA

B. ERA = RAIA

C. ERA = EA + ECEMF

D. ERA = ECEMF/IA

B

Which equation correctly describes the armature voltage?

A. EA = ECEMF - ERA

B. EA = ECEMF + ERA

C. EA = ERA - ECEMF

D. EA = ECEMF × ERA

B

When the motor has no mechanical load, the armature current is generally:

A. Very high

B. Very low

C. Zero in all cases

D. Equal to the field current

C

At no load, when the armature current is very low, ECEMF can approximately be considered equal to:

A. IA

B. RA

C. EA

D. K2

A

When armature current is constant and very low, the relationship between armature voltage and motor speed is:

A. Linear

B. Inversely proportional

C. Exponential

D. Unrelated

B

A DC motor can therefore be considered a:

A. Current-to-voltage converter

B. Voltage-to-speed converter

C. Resistance-to-current converter

D. Speed-to-torque converter

C

In the voltage-to-speed converter, the input is:

A. Motor torque

B. Armature current

C. Armature voltage

D. Motor speed

B

In the voltage-to-speed converter, the output is:

A. Armature current

B. Motor speed

C. Armature resistance

D. Torque

A

A DC motor can also be considered a:

A. Current-to-torque converter

B. Voltage-to-current converter

C. Speed-to-voltage converter

D. Resistance-to-torque converter

C

In the current-to-torque converter, the input is:

A. Armature voltage

B. Motor speed

C. Armature current

D. CEMF

A

In the current-to-torque converter, the output is:

A. Motor torque

B. Motor speed

C. Armature voltage

D. Resistance

A

What is the slope of the speed versus induced voltage ECEMF relationship?

A. K1

B. K2

C. RA

D. IA

B

What is the slope of the torque versus armature current IA relationship?

A. K1

B. K2

C. RA

D. EA

B

If armature voltage increases while armature current remains low and constant, motor speed will:

A. Decrease

B. Increase

C. Stay constant

D. Become zero

B

If armature current increases while armature voltage is fixed, what happens to the voltage drop across RA?

A. It decreases

B. It increases

C. It stays constant

D. It becomes zero

B

If armature voltage is fixed and armature current increases, what happens to ECEMF?

A. It increases

B. It decreases

C. It stays constant

D. It becomes equal to zero immediately

B

If ECEMF decreases, what happens to motor speed?

A. It increases

B. It decreases

C. It stays constant

D. It doubles

B

Therefore, at a fixed armature voltage, increasing armature current causes motor speed to:

A. Increase

B. Decrease

C. Stay constant

D. Become infinite

A

Which sequence is correct when IA increases while EA remains fixed?

A. IA increases → ERA increases → ECEMF decreases → speed decreases

B. IA increases → ERA decreases → ECEMF increases → speed increases

C. IA increases → ERA increases → ECEMF increases → speed decreases

D. IA increases → ERA decreases → ECEMF decreases → speed increases

B

Which statement summarizes the main effect of increasing armature current at fixed armature voltage?

A. Speed increases because CEMF increases

B. Speed decreases because the armature voltage drop increases

C. Speed stays constant because current does not affect the motor

D. Speed increases because resistance decreases

A

What is the primary objective of Laboratory Exercise #7?

A) To demonstrate the main operating characteristics of a separately-excited dc motor using the DC Motor/Generator

B) To analyze the transient response of a series-wound ac motor

C) To measure the efficiency of a three-phase induction generator

D) To test the magnetic saturation limits of a permanent-magnet synchronous motor

B

What alternative term is frequently used for a separately-excited dc motor?

A) Series-field dc motor

B) Independent-field dc motor

C) Compound-wound dc motor

D) Brushless dc motor

B

What is the current flowing in the stator electromagnet of a separately-excited dc motor commonly called?

A) Armature current

B) Field current

C) Residual current

D) Excitation loss current

A

According to Equation (2-2), what is the motor torque T proportional to?

A) The armature current IA

B) The armature voltage EA

C) The armature resistance RA

D) The field current If

A

Under no-load conditions, why can the voltage drop ERA across the armature resistor be neglected?

A) Because the armature current IA has a very low value

B) Because the armature resistance becomes zero

C) Because the field current exceeds nominal limits

D) Because the induced voltage drops to zero

B

When armature current is constant and no mechanical load is applied, what kind of relationship exists between the motor rotation speed n and the armature voltage EA?

A) A non-linear exponential relationship

B) A straight-line linear relationship

C) An inverse logarithmic relationship

D) A sinusoidal relationship

B

When the relationship between EA and rotation speed n is linear, the dc motor can be considered as what type of converter?

A) A current-to-torque converter

B) A voltage-to-speed converter

C) A power-to-frequency converter

D) A resistance-to-voltage converter

A

What kind of converter can a dc motor be considered when looking at the relationship between motor torque T and armature current IA?

A) A linear current-to-torque converter

B) A linear voltage-to-speed converter

C) A non-linear power converter

D) A constant-speed converter

A

According to Equation (2-3), when the armature current IA increases, what happens to the armature voltage EA components?

A) EA equals ECEMF plus the voltage drop ERA across the armature resistor

B) EA equals ECEMF minus ERA

C) EA equals ERA divided by ECEMF

D) EA becomes completely independent of ECEMF and ERA

B

When a fixed armature voltage EA is applied to a dc motor, what happens to the motor rotation speed n as the armature current increases?

A) The speed increases because voltage drop decreases

B) The speed decreases because the voltage drop ERA across the armature resistor increases and causes ECEMF to decrease

C) The speed remains completely constant regardless of armature current

D) The speed drops immediately to zero because the motor stalls